An Orphan in the “Field of Streams”

Belokurov, V.; Evans, N. W.; Irwin, M. J.; Lynden-Bell, D.; Yanny, B.; Vidrih, S.; Gilmore, G.; Seabroke, G.; Zucker, D. B.; Wilkinson, M. I.; Hewett, P. C.; Bramich, D. M.; Fellhauer, M.; Newberg, H. J.; Wyse, R. F. G.; Beers, T. C.; Bell, E. F.; Barentine, J. C.; Brinkmann, J.; Cole, N.; Pan, K. and York, D. G. (2007). An Orphan in the “Field of Streams”. Astrophysical Journal, 658(1) pp. 337–344.



We use Sloan Digital Sky Survey Data Release 5 photometry and spectroscopy to study a tidal stream that extends over ~50° in the north Galactic cap. From the analysis of the path of the stream and the colors and magnitudes of its stars, the stream is ~20 kpc away at its nearest detection (the celestial equator). We detect a distance gradient: the stream is farther away from us at higher declination. The contents of the stream are made up from a predominantly old and metal-poor population that is similar to the globular clusters M13 and M92. The integrated absolute magnitude of the stream stars is estimated to be Mr ~ -7.5. There is tentative evidence for a velocity signature, with the stream moving at ~-40 km s-1 at low declinations and ~+100 km s-1 at high declinations. The stream lies on the same great circle as Complex A, a roughly linear association of H I high-velocity clouds stretching over ~30° on the sky, and as Ursa Major II, a recently discovered dwarf spheroidal galaxy. Lying close to the same great circle are a number of anomalous, young, and metal-poor globular clusters, including Palomar 1 and Ruprecht 106.

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